Heat treatment of chromium alloy steels



TEMPERATURE Dec. 17, 1935. F. M. BECKET El" AL 2,024,561

HEAT TREATMENT'OF CHROMIUM ALLOY STEELS Filed April 9, 1934 ol05% c 0.75% Tl.

24 "C 24 "C D/LA T/ON D/LAT/ ON D/L AT/ON D/LAT/ON D/LAT/ON I D/LAT/ON INVENTORS FREDERICK M. BECKET RUSSEL FRANKS ATTORNEY.

Patented Dec. 17, 1935 .UNITED STATES PATENT OFFICE The invention relates to a proc nm'r mammor cnnomnm Y STEELS Electro Metallurgical of West vil'linla Application April 9, 19:4, Serial No. 719,758

3 Claims. (cl. 148-215) ess of heat treating certain chromium-containing steels, by heating and cooling them, either slowly or rapidly, from temperatures above orbelow those at 5 which the thermal changes ordinarily occur in. the ferritic types of chromium-bearing steels.

When chromium is added to a steel the critical temperature range of the steel is raised appreciably, and the product can be fully softened only by heating for comparatively long periods at temperatures slightly below the critical range, followed by slow cooling. For example, a hot-worked steel containing about 0.12% carbon and 12% chromium cannot be fully softened unless it is held for a period of several hours at temperatures not greater than about 800 C. After holding such steel at this temperature for a suillcient period of time lt'is necessary tocool it slowly in order to attain the softness desired. '20 Such a procedure is carried out to prevent the metalirom air hardening. The extent to which a given steel air hardens depends on its chroing their properties.

is apparent.

Company, a corporation It substantially all of the carbon present in the chromium-bearing metal is in combination with elements such as titanium and columbium, instead of chromium or iron, or both, the steel can be rendered soitand ductile by holding it 5 for a period 01 only a few minutes, instead of hours, at temperatures within a range from somewhat below to somewhat above the normal critical range oi chromium steels. Also, these steels can be cooled from these temperatures 10 either rapidly or slowly without greatly impair- The economic advantage mium and carbon contents. given in Table I.

Table I Percent c: rm: 0 Pucent 'li Condition of mu fiffg" wa 5.75 0. 12 As rolle 4. 80 118 5.70 0.12 Heatedat5500.4hrs.andalrcooled.. 5.50 08 5. 76 0. 12 Hosted at 750 0. 10 min. and air cooled... 7. 50 1G) 5. 75 0. 12 Heated at 750 0. ihrs. and air cooled- 8.00 85 5.76 0.12 at000 0.10 min. and air 4.00 110 5. 03 0. 13 0. 00 As rolled 8. so 35 5.03 0. 18 0.00 Heated at 550 0. 4 hrs. and aircooled-. 8. 10 79 5.08 0.13 0.00 Heated at 750 0. 10 min. and air cooled 8. 80 75 5.08 0.18 0.00 Heatcdat1500.4hrs.andaircooled.- 0.98 58 5.08 0.13 0.00 Heated at 900 0. 10 min, and air cooled 0. 20 7o 18. 00 0. 18 As rolle 5. 00 113 13.00 0.18 Heatedat8500.4hrs.andaircooled- 6.50 08 18.00 0.18 at6500.12hrs. andlurnaee cooled. .3 7. 00 80 18.) 0.13 Heated at 750 0. 10 min. and air cool 50 08 18. 50 0. 18 Heated at 750 C. 4 hrs. and air cooled-- 8. 40 75 18. .018 Heated at 000 C. 10 min. and air cooled 4. 80 112 18.00 0.18 Heated at 1,000 O. 5 min. and air cooled...- 5. 00 mo 13. 85 0. 11 0. 85 As rolled. 8. 10 88 18.85 0. 11 0.85 Heatedat650 G.4hrs.andeircooled 8. 20 88 18.85 0.11 0.85 Heatedat5500.12hrs.andiurnace cooled. 8. 85 81 18.85 0.11 0.85 Heated at 750 0. 10 min. and air 8.00 so coo 18.85 0.11 0.85 Heetedat7500.4hrs.andaircooled.- 0.00 70 18.85 0.11 0.85 Heated at000 0. 10 min. and air cooled 0. 80 70 18.85 0.11 0.85 Heated at 1,000 0.5 min. and air coole 0.40 58 of such a process for annealing chromium steels An object of the invention is to provide a 18 method of heat treating chromium steels wherein substantially all of the carbon present is in combination with titanium or columbium.

The results of a few tests conducted on sheet go steels of twenty gage containing up to about 14% chromium with and without titanium are Table I shows clearly that the titanium-containing steels can be softened by heating for either long or short periods at temperatures below and aoove those at which the critical changes occur in the titanium-free steels. Similar results are obtained when suitable amounts of columbium are substituted for the titanium.

Low carbon steels containing over about 16% chromium are considerably less hardenable than the lower chromium steels. Nevertheless, these high chromium steels are fairly brittle in the rolled state and cannot be rendered sumciently ductile and soft unl-ss they are held for comparatively longer periods at the proper temperatures. As indicated in Table II, the addition of the proper amount of titanium to these steels renders them capable of being made soft and ductile by heating for only a few minutes at temperatures up to about 1000' C.

' AR-l point even more, the latter being brought Referring to Figures 1, -2, a, and 4, it is seen that an-eifect of the titanium or the columbium onsteelsofthe5% chromiumtypeistoraise, considerably the AC-I point, and to raise the nearly to the temperature of the AC1 point.

'Itmaybeseenfromrigures5,and6thatthe addition of titanium to the 13% chromium type practically eliminates the critical changes that normally occur on heating and cooling the titanium-free chromium steels between room temperature and 1000 C.

It is unnecessary in the present invention to maintain a maximum of 0.10% carbon in order to insure maximum softness and workability, because if suitable amounts of titanium are present equally soft steels may be obtained with somewhat higher. carbon. This is clearly demon- Table 11 PeresntCr PcesntO Pu'csnt'li Conditional Bum V 25 18.9 0. Alton- 5.20 N 18.20 0.00 Beatodat7800.ihrs.andaireoolod-- 1.0! 70 18. 0. HUMMW'C. lilmimandsir 0." 83

18.20 0. Heated it 1M 0. 8 min. and .1! 2.70 83 13.00 0.1: 0.78 Asrollsd 1.00 n 30 18.) 0.13 0.78 Hestsdat7li00.4hraandaircooled- ZN 74 1am 0-13 0.78 Kata-It W 0. 10 min. and air 9.1 N eoo 18.1 0.13 0.78 Hfltedatlw G.5min.andair Q/ cooled.

Similar results are obtainable by the use of columbium instead of the titanium.

The effects of titanium and columbium on chromium-steels is further elucidated by dilatostrated by Table III, in which are given the hardness and Erichsen values of 13% chromium steels, low and high in carbon, in the as-rolled state and when heat treated by heating at 1000 C.

metric tests. Dilation curves obtained in tests for five minutes and then air cooled.

7 Table III mm Cr rm: 0 Percent Ti Condition a m W 45 hardness :12: til :22 s; g 13.32 a. 1.76 a, 76 13.32 0.34 1.70 as so 60 11:: use 2.1: u 88 11:2 0.5a 2.1: m m

on chromium steels with and without additions The method of the invention can be a li 55 of titanium and columbium are shown in the accompanying drawing, in which Figure 1 is a dilation curve obtained on a steel containing 5.56% chromium, 0.10% carbon, remainder substantially all iron,

l 'igurezisadilationcurveofasteelcontaining 5.93% chromium, 0.13% carbon, 0.90% titanium, remainder substantially all iron,

Figure 3 is a dilation curve of a steel containing 5.75% chromium, 0.05% carbon, 0.75%

titanium, remainder substantially all iron,

Figureiisadilationcurveofasteelcontainlng 5.85% chromium, 0.10% carbon, and 1.08% columbium, remainder substantially all iron,

Flgure5isadi1ation curveofasteelcontaining 13.17% chromium, 0.12% carbon, remainder substantially all iron,

l 'lguredisadilationcurveofasteelcontaining 13.55% chromium, 0.11% carbon, 0.85% titanium, remainder substantially all iron.

'carbon. When columbium is used, its percentage should be at least six times (and preferably eight to ten times) the carbon percentage. Larger proportions of the softening metal may 70 be used but we prefer that the percentage of titanium or columbium in the sheel shall not exceed its respective stated preferred minimum value by more than 1.5%. 7

We claim:

1. Method 01' heat treating territic steels containing about 4% to 30% chromium; carbon in an amount not over about 0.25%; titanium, the

titanium content being at least about tour timesthe carbon content and being not more than four times the carbon content plus about 1.5%; which method comprises heating the steel to a temperature between about 700 C. and about 1000 C., holding it at said temperature for a time not over about an hour, and then cooling it to room temperature.

2. Method of heat treating territic steels containing about 4% to 30% chromium; carbon in an amount not over about 0.25%; titanium, the

method comprises heating the steel to a temperature between about 700 C. and about 800 (2., holding it at said temperature for a time not over about an hour, and then rapidly cooling it to room temperature.

3. Method of heat treating ferritic steels containing about 4% to 30% chromium;- carbon in an amount not over about 0.25%; titanium, the titanium content being at least about four times the carbon content and being not more than four times the carbon content plus about 1.5%; which method comprises heating the steel -t6"a temperature between about 700 C. and about 800 C., holding it at said temperature for a time not over about an hour, and then air cooling it to 15 room temperature.

FREDERICK M. BECKET. RUSSELL FRANKS. 

